The present invention relates generally to composite structures that are bonded along an interface, and methods of making them. The invention relates more specifically to crystal, ceramic, and glass composites, especially those having relatively large components.
Recently, there is rapidly growing interest in composite materials for solid-state lasers and other optical and electro-optic applications. The prior art includes the following patents:
U.S. Pat. No. 5,441,803 (the '803 patent) describes a method of forming, and constructs of, bonded composites of single crystal materials. The method comprises the steps of optical contacting the surfaces of the single crystal materials selected to form an assembly, bonding the surfaces by gradually heating the assembly to a temperature and for a duration sufficient to effect bonding, and cooling the bonded assembly back to room temperature. No bonding agents are necessary. This patent applies to bonding similar materials such as doped and undoped lasing materials, and also opens the possibility of producing larger crystals than can be grown by conventional crystal growth techniques.
U.S. Pat. No. 5,846,638 (the '638 patent) describes a bonding process for forming defect-free bonds without the use of adhesives as well as devices formed by this method. In general, the disclosed process allows similar or dissimilar crystalline, vitreous or dense polycrystalline ceramic, metallic or organic polymeric components to be first joined by optical contacting and then heat-treated to stabilize the bond. The heat treatment can be performed at a low enough temperature to prevent inter-diffusion between species, thus insuring that the bond is not subjected to excessive mechanical stresses and that the materials do not undergo phase changes. Therefore, stable bonds can be formed using the disclosed process between materials of widely differing physical, mechanical, thermal, optical and electro-optical properties such as different hardness, chemical durability, mechanical strength, CTEs, thermal conductivity, crystal structure, refractive indices, optical birefringence, nonlinear optical properties, electrical conductivity, or semiconducting properties.
With the advent of requirements for high energy lasers for defense and materials processing applications, difficulties arise when components with longer and wider interfaces are to be optically contacted and heat-treated for bonding. It can take several weeks to obtain an optical contact that is free of trapped volatile species at the interface. Subjecting such an interface prematurely to heat treatment may result in complete or partial separation of the components, or in entrapment of impurities and contaminants at the interface or other interface defects.